It is known that glass can be treated to reduce glare (reflection) by making use of two different physical phenomena, diffusion and anti-reflection. Diffusion refers to the phenomenon by which reflections of light are broken up in various directions, so that the intensity of the reflections in the direction of a viewer is reduced, but the total hemispherical reflection remains the same, with "diffusion etching" comprising treating a surface to increase the diffusion effect. Glare reduction by diffusion may be achieved by roughening the glass surface using physical or chemical means, e.g., by grinding, sand blasting, or acid etching. Frosted glass is a typical light diffusion material which is usually made by acid etching of the glass surface. However, such frosted glass cannot be used in applications where high clarity is required along with low glare, for example, in picture frames or as a protective surface for a cathode ray (picture) tube in television receivers or as a screen for computer monitors. In these applications, a high level of clarity is required to prevent distortion of the images and colors displayed by a picture, such as a photograph, or to prevent detracting from the visual appreciation of the image. At the same time, it is also desirable and important to reduce glare to prevent reflected light from interfering with observation of the picture or photograph contained therein. Reduction of glare is of particular importance in computer monitors where fatigue or stress may be induced by unwanted reflections. At the same time, image clarity must be maintained to minimize distortion with consequent eye strain from long-term viewing. While various attempts have been made to improve the light transmission qualities of frosted glass, the degree of clarity that has been achieved in such products has not been sufficient to enable them to be used in picture frames or in monitor screens.
Anti-reflection glass makes use of the destructive interference that results when incident light is reflected from an anti-reflection surface of a glass sheet. By trapping the light at particular wavelengths, there is an actual reduction in the total light reflected, including in the direction of the viewer. Such anti-reflection effects are usually achieved by application to the sheet glass surface of one or more layers of a coating, such as, for example, an inorganic metal oxide, which may be deposited by vacuum deposition, sputtering or sol gel deposition. Although producing a glass surface having low glare and good clarity, these anti-reflection processes are quite costly, and therefore the treated glass is not economical for use in high-volume applications, such as in picture frames, as a replacement for common glass. Consequently, low glare, high clarity sheet glass has not been generally available for use in these applications due to either poor clarity or high cost.